Organotitanium chemistry

A particularly exciting advancement in this field is the enantioselective version as reported by Sharpless 18). Since several reviews 19a f and books 19 J) concerning most of the above reactions as well as additional aspects of organotitanium chemistry have appeared, only brief reference will be made to them here. 

Finally, recent application of organotitanium chemistry to the problem of stereoselective homoaldol condensation (Equation 73) turned out to be highly successful, as reported by Hoppe 123). The threo/erythro ratios (232 233) were better than 97 3 for various aldehydes. 

The bis-//-cyclopentadienyltitanium system has been studied fairly extensively in comparison with other organotitanium species. Bearing in mind some of the challenging and useful aspects of the chemistry of the bis-t -cyclopentadienyl-titanium system,2-4 of interest to include related systems such as the mono-t -cyclopentadienyltitanium one in the expanding examination of organotitanium chemistry. 

Propargylstannanes have usually been prepared by the reaction of a propargylmagne-sium halide with a tin halide,91-92 but the Grignard reagents are not always readily accessible. A more general method makes use of organotitanium chemistry, for example 93... 

The time is apt for chemists to fully enter the world of functionalized organozirconium and organotitanium chemistry. Both of these metal complexes are versatile intermediates due to their ambiphilic nature (1) utilization of these complexes as a source of carbanions (carbon-metal <7-bond) (2) Utilization of these complexes is based on late transition-metal behavior, such as coordination of a carbon-carbon multiple bond, oxidative addition, reductive elimination, j8-hydride elimination or addition reaction [1],... 

Fluoride ion selective spectrometry was used to determine the stability constants for zinc fluoride complexes in water at 25 °C, giving values j3i[ZnF(aq)]+ = 3.5 0.1 and /l2[ZnF2(-aq)] = 3.8 0.5.643 These results demonstrate that the complexation of fluoride is very weak and in aqueous chemistry no species beyond ZnF+ is of much importance. Organotitanium fluorides have been used as matrices for trapping molecular ZnF2 and MeZnF. 4... 

The chemistry of titanium has been reviewed in COMC (1982) and COMC (1995)40 41 as well as in Comprehensive Coordination Chemistry II. 2 Since then, several contributions have covered the coordination chemistry of cyclopenta-dienyltitanium carboxylates and related complexes,43 new titanium imido chemistry,44 the use of titanium(iv) chloride45 and isopropoxide46 in stereoselective synthesis, the preparation and synthetic applications of l, -dicarba-nionic titanium intermediates47 and organotitanium complexes,48 49 and titanium-catalyzed enantioselective... 

There has been no recent comprehensive review of this area, although a book on the organometallic chemistry of titanium, zirconium, and hafnium deals, in part, with some of the hydride derivatives (1). In the present review, the first part of the discussion reflects the fact that much of the early work on organotitanium hydrides was, often unknowingly at the time, interwoven with attempts to prepare titanocene, Cp2Ti (Cp = tj3-C5H5). Subsequent sections deal with similar compounds containing an additional metal (e.g., aluminum), miscellaneous titanium hydride compounds, and a summary of the main properties of the above species. 

The chemistry of organotitanium reagents has b n explored by Reetz, Weidmann and Seebach. The MeLi-TiCU system provides a nonbasic reagent which reacts chemo- and stereo-selectively. Nitro,... 

The organometallic chemistry of titanium is dominated by complexes in the +IV oxidation state and in comparison there are relatively few examples of titanium complexes in the +III oxidation state. For information on organotitanium(iv) see Chapter 4.05. However, examples of titanium(lll) complexes are more common than examples of titanium complexes in lower oxidation states (for information on organotitanium in oxidation states 0 to II see Chapter 4.03) and titanium(m) chemistry is considerably more advanced than the chemistry of the heavier group 4 metals, zirconium and hafnium in the +m oxidation state. For information on organozirconium(m) and organohafnium(m) see Chapter 4.07. 

Organotitanium and -zirconium chemistry already has an established place in organic synthesis and many reactions are covered elsewhere in the Practical Approach series. Examples include reductive coupling of carbonyl compounds with low valent titanium to form 1,2-diols or alkenes methylenation of ester carbonyl groups with titanocene methylidene (Cp2Ti=CH2) zirconium-catalysed methylalumination of alkynes and hydrozirconation of alkynes and alkenes with the Schwartz reagent, Cp2ZrHCl. ... 

Symposia-in-Print - Organotitanium Reagents in Organic Chemistry"... 

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